Allow negative values to count macro arguments from the end (#1670)

test/asm/negative-macro-args.asm

@@ -0,0 +1,21 @@
+MACRO mac
+	for i, -1, -_NARG - 1, -1
+		println "{d:i}: \<i> == \<{d:i}>"
+	endr
+	; error cases
+	def i = 0
+	println "{d:i}: \<i> == \<{d:i}>"
+	def i = -_NARG - 1
+	println "{d:i}: \<i> == \<{d:i}>"
+	def i = $7fff_ffff
+	println "{d:i}: \<i> == \<{d:i}>"
+	; signed/unsigned difference error cases
+	def i = $8000_0000
+	println "{d:i}: \<i> == \<{d:i}>"
+	println "{u:i}: \<i> == \<{u:i}>"
+	def i = $ffff_ffff
+	println "{d:i}: \<i> == \<{d:i}>"
+	println "{u:i}: \<i> == \<{u:i}>"
+ENDM
+
+mac A, B, C, D, E, F, G

test/asm/negative-macro-args.err

@@ -0,0 +1,26 @@
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(7):
+    Invalid bracketed macro argument '\<0>'
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(7):
+    Invalid bracketed macro argument '\<0>'
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(9):
+    Macro argument '\<-8>' not defined
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(9):
+    Macro argument '\<-8>' not defined
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(11):
+    Macro argument '\<2147483647>' not defined
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(11):
+    Macro argument '\<2147483647>' not defined
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(14):
+    Macro argument '\<-2147483648>' not defined
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(14):
+    Number in bracketed macro argument is too large
+while expanding symbol "-2147483648"
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(15):
+    Macro argument '\<-2147483648>' not defined
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(15):
+    Number in bracketed macro argument is too large
+while expanding symbol "2147483648"
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(18):
+    Number in bracketed macro argument is too large
+while expanding symbol "4294967295"
+error: Assembly aborted (11 errors)!

test/asm/negative-macro-args.out

@@ -0,0 +1,14 @@
+-1: G == G
+-2: F == F
+-3: E == E
+-4: D == D
+-5: C == C
+-6: B == B
+-7: A == A
+0:  == 
+-8:  == 
+2147483647:  == 
+-2147483648:  == >
+2147483648:  == >
+-1: G == G
+4294967295: G == >